It’s (Big) Crunch Time

Yes, it’s that end of Science Week – the end when I’m out there spreading the word and explaining weird stuff.

Friday through Sunday is , an hour-long amble through the brain melting fields of Stephen Hawking’s twenty-year-old masterpiece. You should book if you want to come – details on the show’s page – but at the moment there are still tickets left for all three performances (1:30 matinee Friday, 8 PM Saturday and 7 PM Sunday).

Friday evening is Not the Nobel Prize, Melbourne Museum’s science comedy panel show in which four comedians – including myself – go head to head with four scientists. They’ll spin some stories, and we’ll try and decide if they’re true or false. Sadly Sam Simmons can no longer be with us, but joining myself, Courteney Hocking and Charlie Pickering will be the ever-delightful Justin Hamilton. Bound to be excellent! The show starts at 7 PM, and you should book for this one too; details can be found on the Melbourne Museum web site.

And if you need a break from all the exciting Science Week stuff, you can also catch my two improvised projects this week: Impro Sundae with The Crew is on this Sunday, 5 PM at the Bella Union, Trades Hall; and the preview season of Set List, the new improvised musical show from my theatre company Shaolin Punk, plays this Thursday to Sunday night at 9 PM (8 PM on Sunday) at the Butterfly Club. Details can be found via those links, and I should point out that the only one of those in which I’ll be performing is Thursday night’s Set List.

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6 comments

OOOO gravity particles!
That is what is so exciting about gravity. It seems to have no gravity particle (that is detectable) it is monopolar unlike EVERYTHING else and generally seems to be inscrutable in the chinese sense.

I am totally hanging out for this idea to be thrown out the window and explained adequately.

But dont forget, spaghettification (all hail FSM) happens AFTER the event horizon and at that point, all bets are off for einsteinian physics. Like newtons is einsteins equations for large values (ie you can derive netwons laws from einsteins equations), I am sure that einsteins will be a solution to some other more crazy thing yet to come. GUT anyone?

I have made things a bit confusing there, sorry! If we’re describing gravity in the classical Newtonian sense, i.e. as a force, then yes, it acts instantaneously. If there was a delay in it the same way there is with light, the orbits of planets would look very different. In relativity, however, gravity is not a force, but a curvature in space-time caused by massive objects; changes in this curvature are propagated by gravity waves, and these travel at the speed of light. The equations generally agree, though, as it’s only changes in gravity which propagate at the speed of light, and in the case of our astronaut and the black hole, it’s probably safe to assume there’s no significant change in the black hole’s mass, and thus not in its gravitation field, in the time it takes to fall in.

Please note the above is not a final word – it’s just me trying to make sense of all the stuff about gravity! The bottom line is that even in General Relativity, gravity always acts in regards to an object’s current position, without retardation due to light speed delays in propagation.

Note too that some people argue that this does mean gravity waves travel faster than light; some say much faster! They’re outsiders in the current world of physics, though their arguments are fascinating.

Thanks for that answer, it’s good to know- I will have to look up the part of ABHoT that gave me the nightmares to see what Hawking was saying.

When you say ‘gravity is instantaneous’, I was always under the impression that gravity propagated at the speed of light? As in, if the sun suddenly winked out (as happens in one of the Star Trek films), the earth would not be destroyed, or even notice anything was wrong at all, until eight minutes later- the ‘absence of gravity’ would come at the same time as the absence of light. Can any event be instant across multiple frames of reference, and if there is, could that be used to transfer information faster than light?

This isn’t really answered in Hawking’s book, but I’ll have a go – and I’m afraid the other guys were right. Time always seems to flow at the same speed to a particular observer – the clock you keep with you always seems to advance at one second per second no matter your speed or nearby massive objects. The difference in time is only apparent when introducing separate frames of reference. So it would seem the other persons would be right. But now the question is: where is the astronaut’s frame of reference? In her head? What if she’s looking at a watch on her wrist? To get even more specific, precisely where in her head is her frame of reference? It’s true that once you’re close enough to the black hole, even the atoms in the top of her head are experiencing significantly different gravitational effects to those a little lower down! (Truthfully, that’s all rather academic – you’ll be pulled apart physically long before you’re close enough for that to matter.)

The clincher, though, is that the effect of gravity is still instantaneous – however you model it, while light would take more time to reach the astronaut’s head, gravity would reach it at the same time as it reached her legs. So the spaghettification “starts” at both ends at once, with the effect increasing steadily as you fall closer and closer. Now, I know our astronaut is “immortal”, but I can’t think of any form of immortality that could protect you from a black hole, short of being a massless, energy-less consciousness unaffected by gravity. But in that case you won’t be spaghettified at all, and you represent an old-school absolute notion of space and time, and we’re back to square one.

So to summarize: if you’re falling into a black hole, you experience a finite amount of time, slowly getting stretched out, with the stretching getting faster and faster until you finally get torn to bits, probably long before you reach the singularity and oblivion (unless you prefer the Disney movie version of events). The amount of time relies on the mass and therefore size of the black hole (not all black holes are created equal!).

I’m not very familiar with BSG, so their teleport-style FTL travel is news to me, but travel which doesn’t involve going through intervening space breaks a lot of laws of physics! Presumably they wouldn’t experience relativistic time dilation, since no time (or the same, very small amount of time) passes for them and for outside observers during the trip. In that sense, they’re not able to travel into the future, at least not any faster than you or I. They can’t go back in time, either – really, all they can do is “pause” the universe while they travel, and I imagine they can’t affect anything while doing so.

This seems more or less consistent with wormwhole theory; while large, stable wormholes (and these would probably need to be manufactured) might be usable for time travel, that’s only possible if you can drag one end at relativistic speeds, such that the two ends are no longer synchronised in time.

OH! Good questions, I hope that The Man in the Labcoat will answer that for you in his show… 🙂 Otherwise, I am sure that Ben or other readers will be able to help you out here! I might even be able to give it a go.

I’m excited about tomorrow’s show, Ben! Now, at dinner the other night, I overheard someone say: “What happened if you were immortal, but you fell into a black hole?” and I just had to lean over to their table and say: “The same thing that would happen if you were mortal- time would come to a near-standstill, and you’d spend the rest of subjective eternity getting turned into spaghetti. Either way, something to avoid.” This was something I remembered fairly distinctly from ABHoT (it gave me nightmares). However the people I’d rudely interrupted said that time only came to a near-standstill for remote observers- to the person actually being torn apart, time would continue at the same subjective pace as ever. I considered saying: “But their feet would be in a different, more extreme frame of reference from their head, so the phenomenon would still be drawn out over multiple timeframes, making the destruction of the body just as drawn out to the person it was occuring to.” however I felt slightly out of my depth and so withdrew. Could you clarify this issue for me?

Also, now that we’re on the subject, I don’t know if you watch Battlestar Galactica, but like many sci-fi shows if has a form of FTL travel- their ships don’t, like on Star Trek, attempt to gain a velocity greater than lightspeed, they just disappear from one spot and reappear in another. I was trying to tell someone that, even discounting velocity, if you could beat light from one point to another in any form, you could effectively time travel, or at least get information to go backwards in time, thus gaining the ability to cause paradoxes (someone sending themselves a message not to send the message in the first place, for example). However when pressed to explain myself, I found that I couldn’t. Is this question answerable, or have I just got my wires crossed? We can discuss this in person if you’re not catching my drift.